This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Breast cancer is one of the most common cancers among women worldwide. In order to lower the death rate due to breast cancer, significant improvements in the areas of screening, diagnosis, and therapy monitoring of cancer are imperative. Diffuse optical imaging and spectroscopy methods promise new tools for these applications. The optical methods utilize non-ionizing radiation (e.g. red to infrared light), are non-invasive or minimally-invasive, and are inexpensive, technologically simple and fast. These methods provide several unique parameters based on functional processes in tissues with potential to enhance breast tumor sensitivity and specificity. Tissue optical absorption coefficients provide access to blood dynamics, total hemoglobin concentration, blood oxygen saturation, water concentration and lipid content. These tissue properties are often substantially different in rapidly growing tumors;for example, high concentrations of hemoglobin with low oxygen saturation are suggestive of rapidly growing tumors due to their high metabolic demand and (sometimes) poor perfusion. In a different vein, an increase in organelle population, particularly mitochondria or nuclei, sometimes accompanies the higher metabolic activity of the rapidly growing tumor, and leads to an increase of optical scattering coefficients for the tumor. Finally, optical absorption, fluorescence, and scattering of exogenous contrast agents that occupy vascular and extravascular space also provide useful forms of sensitization. Along these lines, advances in diffuse optical imaging of breast are critical for exploitation of advances in the field of Molecular Imaging, an emerging area of medicine promising development of new generation contrast agents.